In full screen, mouse cursor switches to host mouse when is on top

When enabled full screen mode, if I point the cursor on a strip of half inch from the top, the image of the cursor switches to image of the host mouse cursor and it turns no longer functional -so it's impossible to close or restore windows and so on, but its movement has continuity- in the guest (only when remains in that strip)

However if I disable mouse integration it becomes fully functional over all screen.